1. Field of the Invention
The present invention relates to a control apparatus for generating control signals for controlling operation of an internal combustion engine by effecting a timing control on the basis of identified reference positions corresponding to individual engine cylinders, respectively. More particularly, the present invention is concerned with a control apparatus for an internal combustion engine which can rapidly perform the cylinder identification to be reflected onto the timing control with a simplified structure while deriving a reference position signal relating to a crank shaft with high reliability to thereby ensure an enhanced accuracy for the timing control and which apparatus is capable of executing a backup control even in the case where the angular position signal indicating angular position of the crank shaft can not be obtained (i.e., even when a failure occurs in a first signal series mentioned hereinafter).
2. Description of Related Art
In general, in a control system for an internal combustion engine (hereinafter also referred to simply as the engine), there are employed a reference position signal and a cylinder identifying signal generated in synchronism with rotation of the engine for the purpose of controlling such parameters as the ignition timing, amount or quantity of fuel to be injected (hereinafter also referred to as the fuel injection quantity) and others. Usually, the signal generator for generating these signals is mounted on a cam shaft of the engine and structured such that one-to-one correspondence to the engine cylinders can be established for thereby detecting indirectly rotation or angular positions of a crank shaft.
For having better understanding of the present invention, technical background thereof will be descried in some detail. FIG. 8 is a perspective view showing a mechanical assembly of a rotation signal generator employed in a hitherto known engine control system, and FIG. 9 is a circuit diagram showing an electric signal processing circuit provided in association with the assembly shown in FIG. 8. For more particulars, reference may be made to Japanese Unexamined Patent Application Publication No. 68252/1994 (JP-A-6-68252). In this conjunction, it is assumed that the internal combustion engine now of concern has six cylinders.
Referring to FIG. 8, a cam shaft 1 is rotated at a speed equal to a half of the rotation speed (rpm) of a crank shaft (not shown) so that the control timings for all the six cylinders can fall within a single rotation of the cam shaft 1.
More specifically, a rotating disk 2 fixedly secured to the cam shaft 1 so as to corotate therewith is formed with a series of radial slits 3a in an outer peripheral portion of the rotating disk 2 with equal angular distance therebetween for generating an angular position signal POS composed of a series of pulses generated at every predetermined angle in the course of rotation of the rotating disk 2. Additionally, the rotating disk 2 is formed with a number of windows 3b (six windows in this case) for generating reference position signals REF in one-to-one correspondence to the engine cylinders, respectively.
A light emission diode (LED) 4a is disposed fixedly at a position facing a circular array of the slits 3a, while a light emission diode (LED) 4b is fixedly disposed at a position facing a circular array of the windows 3b. Further, photodiodes 5a and 5b are fixedly disposed in opposition to the light emission diodes 4a and 4b, respectively, with the rotating disk 2 being interposed therebetween, wherein the light emission diode 4a and photodiode 5a cooperate to constitute a first photocoupler while the light emission diode 4b and the photodiode 5b constituting a second photocoupler.
Now, referring to FIG. 9, amplifier circuits 6a and 6b are connected to output terminals of the photodiodes 5a and 5b, respectively, while connected to the output terminals of the amplifier circuits 6a and 6b are output transistors 7a and 7b, respectively.
As can be appreciated from the above, the rotating disk 2, the photocouplers 4a; 5a and 4b; 5b, the amplifier circuits 6a and 6b and the output transistors 7a and 7b constitute a rotation signal generator 8 for generating the angular position signal POS and the reference position signal REF.
FIG. 10 is a block diagram showing an engine control system known heretofore. Referring to the figure, the angular position signal POS and the reference position signal REF outputted from the rotation signal generator 8 are supplied to a microcomputer 10 by way of an interface circuit 9 to be arithmetically processed for controlling the ignition timing, the fuel injection quantity and others.
FIG. 11 is a waveform diagram for illustrating the angular position signal POS and the reference position signal REF outputted from the rotation signal generator 8.
Referring to the figure, the angular position signal POS is comprised of a series of pulses generated in correspondence to the slits 3a, respectively, formed in the rotating disk 2, wherein each of the pulses of the angular position signal POS is generated, for example, at every crank angle of 1.degree.. Thus, the angular position signal POS can be used for determining or measuring the angular position of the crank shaft. On the other hand, the reference position signal REF has a pulse sequence repeated upon every rotation of the crank shaft for a crank angle of 720.degree.. More specifically, the pulse sequence of the reference position signal REF includes six pulses each rising up at a predetermined crank angle in correspondence to each of the engine cylinders, wherein the six pulses have respective pulse widths which differ from one to another engine cylinder so that they can be used as the cylinder identifying signals, respectively. Needless to say, the pulses of the reference position signal REF having the different pulse widths or durations can be generated, for example, by changing correspondingly the circumferential length of the windows 3b, respectively.
The conventional engine control system implemented in such structure as described above by reference to FIGS. 8 to 10 can discriminatively identify the individual engine cylinders and the reference positions (reference crank angles) on the basis of the angular position signal POS and the reference position signal REF for effectuating optimal control of the ignition timing, the fuel injection quantity and others in dependence on the engine operation states.
However, because the cam shaft 1 is driven from the crank shaft (not shown) by way of a transmission mechanism such as a transmission belt/pulley mechanism (not shown either), there may arise a phase difference in rotation between the cam shaft 1 and the crank shaft, although it depends on the engine operation state. As a result of this, the angular positions indicated by the angular position signal POS and the reference position signal REF generated by the rotation signal generator 8 may undesirably be deviated or offset from the actual crank angle. Accordingly, when the engine operation control is performed on the basis of the signals suffering the phase deviation, the control of the ignition timing and other will naturally be accompanied with corresponding deviation or error, making it difficult or impossible to obtain the engine operation performance as intended.
To cope with the problem mentioned above, there has already been proposed such an apparatus which is so implemented as to generate the angular position signal POS and the reference position signal REF with high accuracy in association with the crank shaft while generating only the cylinder identifying signals bearing one-to-one correspondence to the individual engine cylinders, respectively, in association with the cam shaft 1, as is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 68252/1994 (JP-A-6-68252).
However, the engine control system disclosed in the above publication suffers shortcomings in that the sensor as well as peripheral devices thereof provided in association with the crank shaft for generating the angular position signal POS and the reference position signal REF is much complicated and expensive and that a great difficulty is encountered in realizing a backup control in the case where either one of the angular position signal POS or the reference position signal REF becomes unavailable due to occurrence of abnormality or fault in the sensors provided in association with the crank shaft, incurring possibly shutdown of the engine operation.
As is apparent from the foregoing, the engine control system known heretofore suffers a problem that the detection accuracy of the angular position signal POS and the reference position signal REF is impaired when the rotation signal generator 8 is provided in association with the cam shaft 1 because of possibility of the phase difference in rotation between the rotation signal generator 8 and the crank shaft, as a result of which deviation or error is involved in the control of the ignition timing and other, presenting a great obstacle in realizing the performance as intended.
On the other hand, in the case of the engine control system such as disclosed in Japanese Unexamined Patent Application Publication No. 68252/1994 (JP-A-6-68252) where the angular position signal POS and the reference position signal REF are generated by the sensor device provided in association with the crank shaft, while the cylinder identifying signal is generated by the means provided in association with-the cam shaft, there arises problems that the sensor and peripheral devices provided in association with the crank shaft are much complicated and that the backup control can not be carried in the case where the angular position signal POS or the reference position signal REF becomes unavailable.